Hopes for the Copenhagen climate summit in December have been boosted after it emerged that more than 60 presidents and prime ministers plan to attend.
There is concern that no legally binding treaty will emerge from the 7-18 December talks in Copenhagen.
But observers say the presence of so many leading government figures will radically increase expectations.
The annual UN climate change talks are usually conducted by countries' environment ministers.
Delegations from 192 countries will be attending the summit, which will attempt to draw up a new global climate treaty to supplant the UN's 1997 Kyoto Protocol.
UK Prime Minister Gordon Brown, who will be attending, has said a new deal will be more likely if heads of governments put their own reputations on the line.
Australian Prime Minister Kevin Rudd, who will be a key negotiator at the summit, has said he believes those involved in the summit are capable of reaching a non-binding political agreement that would be codified sometime next year.
"I believe there is a strong and high degree of political resolve from many of the leaders around the world to land a Copenhagen agreement," he told the BBC.
But he said reaching what he called an "operational framework agreement" was "not inevitable" and that the negotiations will be "very tough".
Australia is the world's largest exporter of coal and has the highest per capita emissions of any developed nation, but Rudd has said he wants to be part of the solution.
He says every nation will be entering the talks with dirty hands so that should not stand in the way of an agreement.
The leaders of China, the US and India - some of the world's biggest polluters - are so far not on the list to attend the Copenhagen meeting.
'Violated'
The news comes as a row continues over e-mails between climate scientists which were stolen from a British university computer.
Climate sceptics say the e-mails, stolen by a hacker from the University of East Anglia, show that important data behind the climate change debate has been manipulated.
The scientists behind the research say the scientific debate about climate change is sound and have accused the sceptics of trying to undermine Copenhagen.
Critics say the e-mails show that scientists have distorted the facts of climate change, but Mr Trenberth said the e-mails had been "taken out of context".
